Mesenchymal stem cells (MSCs) are the formative pluripotential blast cells found inter alia in bone marrow, blood, dermis and periosteum that are capable of differentiating into more than one specific type of mesenchymal or connective tissue (i.e. the tissues of the body that support the specialized elements; e.g. adipose, osseous, stroma, cartilaginous, elastic and fibrous connective tissues) depending upon various influences from bioactive factors, such as cytokines. The potential to differentiate into cells such as osteoblasts and chondrocytes is retained after isolation and expansion in culture; differentiation occurs when the cells are induced in vitro under specific conditions or placed in vivo at the site of damaged tissue.
Epitopes on the surface of the human mesenchymal stem cells (hMSCs) are reactive with certain monoclonal antibodies known as SH2, SH3 and SH4 described in U.S. Pat. No. 5,486,359. These antibodies can be used as reagents to screen and capture the mesenchymal stem cell population from a heterogeneous cell population, such as exists, for example, in bone marrow.
Hematopoietic stem cells (HSCs) are the formative pluripotential blast cells found inter alia in bone marrow and peripheral blood that are capable of differentiating into any of the specific types of hematopoietic or blood cells, such as erytlirocytes, lymphocytes, macrophages and megakaryocytes. The expression of a particular antigen or antigens on the cell surface or in the cytoplasm and the intensity of expression indicate the stage of maturation and lineage commitment of the hematopoietic stem cell. Human hematopoietic stem cells (hHSCs) are reactive with certain monoclonal antibodies, such as CD34, recognized as being specific for hematopoietic cells.
Thus, human hematopoietic stem cells and human mesenchymal stem cells have been readily distinguishable by their immunospecific profiles.
The present invention provides a population of human mesenchymal stem cells enhanced in cells that are positive for CD45 antibody markers. As hereinafter indicated, a mesenchymal stem cell is one which is capable of differentiating into more than one specific type of mesenchymal tissue cell. Applicants have provided a population of precursor mesenchymal stem cells (xe2x80x9cpre-MSCsxe2x80x9d) which is positive for CD45. These precursor mesenchymal stem cells can differentiate into the various mesenchymal lineages, for example, the chondrocyte, adipocyte and osteoblast lineages.
In another aspect, the present invention provides a population of human mesenchymal stem cells that are CD45 positive and positive for at least one of the SH2, SH3 or SH4 markers. The mesenchymal stem cells of the present invention are preferably positive for at least the SH3 marker. In another aspect, the precursor mesenchymal stem cells are positive for the SH2 marker.
These precursor mesenchymal stem cells may be obtained using antibodies to markers of mesenchymal and hematopoietic cells. Unexpectedly, it was found that a significant number of cells positive for select markers of mesenchymal stem cells were further characterized as being CD45 positive. CD45 is a marker commonly found on leukocytes and hematopoietic cells and not on cultured mesenchymal stem cells. Although not intending to be bound by any theory, it is believed that the population of cells of the present invention comprises a precursor cell to more mature, though not committed, mesenchymal stem cells.
The invention further provides a method for recovering an isolated population of CD45+ human mesenchymal stem cells from bone marrow or other mesenchymal stem cell source of an individual by (i) obtaining bone marrow tissue or other tissue source of mesenchymal stem cells from a donor; (ii) isolating a population of cells enriched in mesenchymal stem cells therefrom; and (iii) further selecting CD45+ cells from the population of human mesenchymal stem cells to obtain a population of mesenchymal stem cells that are enriched in CD45+ mesenchymal stem cells.
In a further aspect, the invention provides a method for recovering an isolated population of CD45+ human mesenchymal stem cells that are also positive for at least one of SH2, SH3 or SH4 markers from bone marrow or other mesenchymal stem cell source of an individual by (i) obtaining bone marrow tissue or other source of mesenchymal stem cell from a donor (ii) isolating a population of cells enriched in mesenchymal stem cells therefrom; (iii) selecting from the cell population a population of mesenchymal stem cells that are positive for at least one of SH2, SH3 or SH4 markers; and (iv) further selecting CD45+ cells from the population of human mesenchymal stem cells of step (iii) to obtain a population of mesenchymal stem cells that are positive for at least one of either SH2, SH3 or SH4 markers and CD45+. In a preferred embodiment, the CD45 cell population is at least SH3 positive.